header {
  ul {
    & > li:nth-of-type(2) > a {
      color: #fff;
    }
  }
}

main {
  width: 100%;
  padding-top: 150px;
  background-color: #f6f8fa;
  .main-bottom {
    width: 100%;
    height: 450px;
    display: flex;
    justify-content: center;
    ul {
      position: relative;
      width: 1200px;
      & > li {
        vertical-align: top;
        width: 23%;
        font-size: 0;
        transition: all 0.3s;
        background-color: #ddd;
        // margin: 10px;
        // overflow: hidden;
        & > img {
          width: 100%;
          height: 100%;
          display: inline-block;
        }
      }
    }
  }
}
